How to do: 90/90 Rotational Sit-Up

Begin in the same position as the previous exercise, but this time bend the elbows and bring the arms in towards the torso. As the legs drop to one side, you’ll travel with the movement of the legs, rolling on to your side briefly before sitting up into a flexed position over the top of your legs. Reverse the movement and repeat on the opposite side. Alternate sides for 10 reps each direction.